The present invention relates to a time-division multiple access communication system in which user packets are transmitted on a randomly selected timeslot for accessing a central station. Specifically, this invention relates to a contention technique associated with collision of data due to simultaneous packet transmissions from contending users. The present invention is particularly suited for satellite communications systems.
With a random access satellite communication system using slotted time intervals, known as the slotted ALOHA system, short-delay communication is possible between a user terminal and a central host computer when the rate of message occurrences is relatively low. However, with an increasing rate of message transmissions, data collisions occur with an increasing rate. Under such circumstances, it is likely that retransmissions encounter collision with new packet transmissions, and the channel utilization efficiency of the system is severely degraded. This problem arises from the fact that, since each user station has no knowledge on the status of every timeslot of the access channel, it is impossible for user stations to control their packet transmissions when a data collision occurs between other stations.